Patent GB-295236-A (GB)
Title: Improvements in repeatered transmission lines for telephone systems
IPC: H04M3/40
Filed: 1927-05-04
Abstract: 295,236. Standard Telephones & Cables, Ltd., (Western Electric Co., Inc.). May 4, 1927. Addition to 264,593. Manual and semi-automatic exchange systems. - In a system of the kind described in the parent Specification in which a twoway telephonic repeater is inserted automatically between incoming and outgoing toll lines as a result of plugging in by the operator, the lines are arranged in groups, while the cord circuits and in some cases the repeater are also divided into groups. Figs. 1, 9, and 10 shows the layouts of three arrangements, in each case the repeater being selected by a switch associated with the group to which the cord circuits belongs, and the total lines then being connected by non-numerical switches to the selected repeater. The arrangement of Fig. 1 is described in detail. Establishment of toll call. An incoming call over the line A is indicated to the inward operator by the lighting of lamp 200 and she plugs into jack 201. If a through connection is required, she transfers the call to the through operator's position. This is effected in the toll cord circuit C by operation of transfer key 405, which connects relay 406 with a parallel resistance over the ring of plug 400, (relay 411 being energized over talking key 401) to relays 210, 211. Only relay 211 energizes in this circuit, and lights lamps 202 in place of 200. The through operator plugs into jack 203, and throws talking key 401 to energize relay 411. In the sleeve circuit, relays 218, 422 are now energized, while marginal relay 423 is inoperative. Relay 431 extends the. line A to the operator's set. The call is set up in the usual manner, and relay 441 energizes in the sleeve circuit, while marginal relay 470 is inoperative. Ringing is effected by means of key 435, which controls a circuit over the tip of plug 403 for a ringing relay. Seizure of an idle repeater. The increased resistance of the slesve circuit when key 401 is thrown causes previously-energized marginal relav 219 to fall back, and relay 217 energizes momentarily, connecting battery to the sleeve circuit to release relay 422. This results in the energization of relay 430, which locks, while relay 439 is energized in a similar manner through the medium of the sleeve circuit of the outgoing line. These relays cause the operation of the cord finder D to make connection with the cord circuit C, when relay 504 energizes and connects up relays 509, 510, 503, which serve to prevent interference from cord circuits of the same or any other group. The repeater selector F now operates to select an idle repeater G, and relay 440 energizes and locks to mark the repeater engaged. Connection of repeater to incoming and outgoing lines. The energization of relay 440 causes a momentary operation of relay 416, which connects ground through low and high resistances 457, 458 to the sleeve circuits. The effect of this in the incoming line is to energize relay 226, which locks and starts the trunk finder H in search of an idle repeater finder K having access to the incoming ends of repeaters, which is indicated by ground over bank 301, test relay 231 being connected to battery over a front contact of relay 228. An idle repeater finder M having access to the outgoing ends of repeaters is indicated by battery, and in the case of the outgoing line, the test relay is connected to ground over a back contact of the relay corresponding to 228, which is inoperative on account of the high resistance 458 connected to the sleeve circuit. Relay 302 energizes, and vertical magnet 320 of the finder K interacts with relay 318 until the tens terminal 305 marked by relay 525 is reached. Change-over relay 322 then energizes and connects in rotary magnet 319, which operates until the terminal 330 marked by relay 522 is reached, when relay 321 energizes and connects up switching relay 316. A.C. is connected up to reduce the resistance at the terminals as in the parent Specification. The outgoing line is connected to the repeater G over finders similar to H, M. In response to the restoration of talking key 401, relay 531 energizes and prepares the repeater G for transmission, while relay 242 and the corresponding relay of the outgoing line operate to complete the connection through the repeater. Supervision takes place as in the parent Specification. Abnormal conditions. 'When the cord finder D has made connection to the cord circuit C, relay 512 energizes and starts a timing switch T. If an idle repeater is not found within a predetermined time, relay 445 energizes and releases the cord finder. An alarm is given and supervisory lamps 413, 437 are flashed. If all the repeaters are in use, all relays like 514 are energized, so that there is no direct battery for operating relay 440, but relays 550, 469 energize (being no longer short-circuited), operating a statistical meter R and flashing lamp 437. If no tens terminal of a repeater finder is marked, the finder is released.